The present invention relates generally to winding apparatus, and more particularly to a novel winding apparatus for manufacturing wound cores of the type employed in electric transformers and the like.
Recent developments in transformer technology have created the need for irregular shaped transformer cores made of layers of ribbon wound directly atop one another about irregularly shaped mandrels of various sizes. One type of transformer core used in magnetic switching and pulse compression apparatus is made of layers of conductive magnetic ribbon wound in the shape of an elongated loop with straight parallel sides and semicircular ends. In some of these transformer cores, insulating ribbon is interleaved with the conductive ribbon as the core is wound. One type of conductive ribbon used in such cores is METGLASS, a non-crystalline, tension-sensitive magnetic ribbon developed by Allied Industries. The tension-sensitive nature of the ribbon can make winding difficult because application of longitudinal tension during winding in excess of a certain limit may detrimentally alter the magnetic properties which are essential to the function of the ribbon.
In manufacturing wound cores it is desirable that the successive layers be aligned directly over one another and be tightly packed so as to prevent relative movement between the layers and maintain their alignment. When winding a core having planar outer surfaces formed by generally planar surfaces on the mandrel, obtaining desired tightness between successive layers along the planar portions of the mandrel is difficult due to the tendency of air to accumulate between successive layers of the winding. This problem is not encountered at the outwardly curved portions of the mandrel because the tension on the ribbon as it is applied urges it against the curved underlying surface in a manner to progressively force the air from between the wound layers and thereby enable tight packing of the ribbon. However, along generally planar surface portions of the mandrel, the ribbon tension does not urge the ribbon against the underlying surface in the same manner, and air may be captured between successive layers of ribbon so as to cause the winding to bulge outwardly. Increasing the tension on the ribbon may reduce the bulging somewhat, but the tension-sensitive nature of the ribbon limits the tension which may be applied to accomplish this. Known winding machines have not been capable of satisfactorily manufacturing irregular shaped windings of the aforementioned type due to their inability to maintain the windings tightly packed.